When a defective portion such as a void, a crack or the like is present in an insulator (for example, an insulator used for wire coating) provided in a high-voltage apparatus, it is known that the electric field is concentrated in the defective portion during operation of the high-voltage apparatus and a feeble discharge called a partial discharge occurs.
If the operation of the high-voltage apparatus continues in a state in which a partial discharge has occurred, the void or crack develops and a dielectric breakdown occurs, which may lead to a failure of the high-voltage apparatus. Thus, before a dielectric breakdown occurs, detecting a partial discharge suitably as a sign phenomenon thereof is demanded.
As one detection technique of a partial discharge, the AE method that detects acoustic emission waves (hereinafter, called AE waves) can be cited. An AE wave is an elastic wave (acoustic wave) generated by energy stored in an insulator or the like. An AE wave is emitted from the defective portion when a partial discharge occurs and thus, a sign of the dielectric breakdown can be known by detecting the AE wave.
For example, PTL 1 describes an insulation failure diagnostic apparatus that diagnoses the presence/absence of a partial discharge (insulation failure) of a high-voltage apparatus based on the detection value of an AE sensor. The above AE sensor is installed in a housing in which the high-voltage apparatus is housed.